The present invention relates to a lithographic printing plate support and a method of manufacturing the same. More specifically, the invention relates to a lithographic printing plate support capable of obtaining a presensitized plate for lithographic printing which is excellent in scratch resistance and achieves a good balance between sensitivity and press life, and a method of manufacturing the same.
Lithographic printing is a process that makes use of the inherent immiscibility of water and oil. Lithographic printing plates used in lithographic printing have formed on a surface thereof regions which are receptive to water and repel oil-based inks (referred to below as “non-image areas”) and regions which repel water and are receptive to oil-based inks (referred to below as “image areas”).
The surface of the aluminum support employed in a lithographic printing plate (referred to below simply as a “lithographic printing plate support”) is used to carry non-image areas, and must therefore have a number of conflicting properties, including, on the one hand, excellent hydrophilicity and water retentivity and, on the other hand, excellent adhesion to the image recording layer that is formed thereon. If the surface of the lithographic printing plate support is not hydrophilic enough, ink will adhere to non-image areas during printing, causing ink buildup on the blanket cylinder and, in turn, scumming. That is, the scumming resistance of the plate will worsen.
Scratch-like dropouts occur on an image due to striking of a presensitized plate against something when it is handled, slight rubbing of the presensitized plate against interleaving paper, or slight touching as touching a plate surface by a finger, and hence its handling during the plate making operation is now difficult. In order to enhance the scratch resistance, attempts have been made to lower the coefficient of friction by forming a layer made of a fluorochemical surfactant or a waxing compound on the surface of a recording layer. However, a satisfactory solution has not been obtained yet.
The smoother the surface of the lithographic printing plate support is, the smoother the recording layer formed thereon is, hence the more excellent the resulting lithographic printing plate is in scratch resistance. However, if the surface of the lithographic printing plate support is too smooth, adhesion of the lithographic printing plate support to the recording layer is impaired, which readily causes the recording layer to come off, thus leading to deterioration of the durability (press life) when a large number of impressions are made.
When locally deep recesses are formed on the surface of a lithographic printing plate support, a lithographic printing plate having a positive-type image recording layer formed on the support has a problem that locally deep portions in non-image areas are not readily developed, whereas a lithographic printing plate having a negative-type image recording layer formed on the support has a problem that image is not readily formed in locally deep portions of image areas, leading to lowering of the sensitivity.
In order to enhance various performance characteristics such as scumming resistance, scratch resistance, sensitivity and press life, asperities are formed on the surface of the lithographic printing plate support through various surface graining treatments.
JP 2003-112484 A (the term “JP XXXX-XXXXXX A” as used herein means an “unexamined published Japanese patent application”) describes a lithographic printing plate support which is obtained by subjecting an aluminum plate to graining treatment and anodizing treatment and which has on the surface thereof a grained shape of a structure in which a small wave structure having an average aperture diameter of 0.01 to 0.2 μm is superposed on a medium wave structure having an average aperture diameter of 0.5 to 5 μm. JP 2003-112484 A also describes that the lithographic printing plate obtained is excellent in press life and scumming resistance.
JP 2003-1963 A describes a method of obtaining a presensitized plate for use in laser plate making which is excellent in press life and does not cause scumming on the blanket cylinder or printing paper, the method using a lithographic printing plate support obtained by subjecting an aluminum plate to mechanical graining treatment in which the aluminum plate is scrubbed with rotating brushes while abrasive particles having a mean particle size of 5 to 70 μm and containing at least 60% by mass of SiO2 are supplied thereto; etching treatment; and electrolytic graining treatment in which the aluminum plate is electrolyzed in an acidic electrolyte solution.
JP 2004-148798 A describes a lithographic printing plate support which has a surface area ratio ΔS50 defined by formula (11):ΔS50(%)=[(Sx50−S0)/S0]×100(%)  (11)wherein Sx50 is the actual surface area of a 50 μm square surface region as determined by three-point approximation from three-dimensional data on the surface region measured with an atomic force microscope at 512×512 points and S0 is the geometrically measured surface area of the same surface region, of 50 to 90%, and which has a steepness a 4550(0.02-0.2), defined as the surface area percentage represented by areas where the slope is 45° or more in the data obtained by extracting the 0.02 to 0.2 μm wavelength components from the above three-dimensional data, of 5 to 40%.